1. Field of the Invention
The present invention relates generally to a method of manufacturing a coffee extract allowing a long-term preservation, and more particularly to a coffee extract manufacturing method, allowing a long-term preservation of a coffee extract that has a high concentration of solid content and is diluted for drinking.
2. Description of the Related Art
Some components in coffee extract become insoluble and precipitate during long-term preservation. The amount of precipitation is especially large in coffee extract which has high concentration of solids content and is diluted for drinking, and this reduces the value of the product. This precipitation occurs even during refrigeration, and accelerates in ordinary temperature.
The precipitation of insoluble components in coffee extract proceeds from the decline of hydrogen ion exponent (pH), which causes not only precipitation or cloudiness in coffee extract but also deterioration of flavor accompanied with increase of sourness.
Therefore as a method of preventing this precipitation and deterioration of flavor, there has been proposed a manufacturing process containing addition of sodium hydrogen carbonate into coffee extract(Japanese Patent Laid-open Pub. Nos. 61-74543, 2-222647, 6-2925).
However, if coffee extract is filled into a sealed container, the use of a large quantity of alkaline carbonate, such as sodium hydrogen carbonate mentioned above, causes gas because of long preservation or heat sterilization with the result that the container expands to deform and break. The invention purposes to solve these problems and has achieved its purpose by the completion of the invention mentioned below.